Previous direct field sound masking systems have used a single, often quite small, controller to drive hundreds of loudspeaker emitters, which can cover thousands of square feet with sound masking. Such systems can, for example, be of the type taught in U.S. Pat. No. 7,194,094 B2 of Horrall et al., the teachings of which patent are incorporated by reference in their entirety. The foregoing qualities of such systems are possible because of the very low power needed for direct field sound masking as compared with the power and costs of in-plenum systems. Such direct field sound masking systems can use readily available cabling and a simple installation process.
Unfortunately, there are some situations in which such existing direct field systems have drawbacks for achieving real paging capability, without using a duplicate sound system. Also, because low frequency response is sacrificed for economy, size, and power, it is sometimes not possible to extend the sound masking spectrum to low frequencies, such as below about 250 Hz.
Louder paging and lower frequencies require more power at each emitter, which is not consistent with the architecture of existing direct field systems. Desired ideal paging levels would require about 100 times the level achieved by existing systems, or 100 times the power. This would require an entirely different system than existing direct field systems. The power required in a central controller for these power levels would be hundreds of watts and simply would not be an efficient or cost effective solution.